1. Field of the Invention
The present invention relates to a printing apparatus, a method of controlling the same, and a storage medium.
2. Description of the Related Art
In a conventional printing apparatus, an unfixed toner image transferred onto a sheet is fixed by a fixing device including a rotatable heating roller and a rotatable pressure roller. In the fixing device, the sheet is heated and pressed while causing the nip formed by the pressure roller in pressure contact with the heating roller to sandwich and convey therethrough the sheet having the unfixed toner image formed thereon, whereby the toner image is fixed on the sheet. As can be understood from the above-described operation, it is desirable that the fixing device is configured to heat and melt the whole of an unfixed toner image transferred on a sheet and then fix the same on the sheet.
However, when half melted toner, overmelted toner, toner having electrostatically adhered to the heating roller, or the like exists, the toner is transferred as toner soil to the pressure roller via the heating roller. Then, when toner soil is accumulated on the pressure roller, a sheet easily sticks to the pressure roller, so that a sheet can be wound around the pressure roller, or a sheet can be soiled by the accumulated toner soil.
To solve this problem, there has been proposed a method in which a cleaning sheet is passed through a fixing device so as to remove toner soil from a pressure roller (see e.g. Japanese Patent Laid-Open Publication No. 2001-22216).
Japanese Patent Laid-Open Publication No. 2001-22216 discloses two cleaning methods.
In the first cleaning method, a cleaning sheet having a solid black image printed on one side thereof is passed through a nip formed between a heating roller and a pressure roller, in a state where the surface printed with the solid black image faces the pressure roller. This makes it possible to cause toner soil on the pressure roller to adhere onto the cleaning sheet, whereby it is possible to remove the toner soil from the pressure roller. This method utilizes differences in adhesion of toner soil remaining half melted on the pressure roller to the sheet, the pressure roller, and the solid black image.
In the second cleaning method, when a cleaning sheet is nipped by a nip, rotation of the heating roller and the pressure roller is stopped, and the nip is heated. Then, the heating is stopped after soil on the pressure roller held in pressure contact with the heating roller via the cleaning sheet is fully melted, and then after the sheet in the nip and the pressure roller are cooled as appropriate, the heating roller and the pressure roller are rotated to bring a next cleaning portion of the pressure roller to the nip. This sequence of operations is performed as one step, and the same step is repeatedly carried out, whereby it is possible to remove toner soil from the pressure roller.
It is desirable that a cleaning sheet for use in the above-described cleaning method has a width close to that of the pressure roller or the heating roller so as to remove toner soil from the pressure roller or the heating roller. For this reason, the user sets a sheet having the width close to the pressure roller in a sheet feeder of the printing apparatus before cleaning. This makes it possible to minimize the amount of toner soil on the pressure roller left unremoved by the toner soil removal operation.
Japanese Patent Laid-Open Publication No. H08-328421 discloses an image forming apparatus which prompts the user to set a cleaning sheet when a toner remaining amount becomes equal to or smaller than a predetermined amount or after a paper jam has been detected, and then automatically cleans a fixing device by feeding the set cleaning paper. According to this apparatus, it is possible to automatically perform cleaning without receiving a cleaning instruction manually given by the user.
However, in a job for executing next printing after completion of cleaning operation using a cleaning sheet, printing is not always performed on a sheet having the same size as that of the cleaning sheet. For example, there is a case where the size of a sheet that can be used for cleaning is A4, and the size of a sheet to be used for printing after the cleaning is A5. In this case, if the printing apparatus executes the next print job immediately after completion of the cleaning, there is a fear that the sheet having a size not intended by the user might be fed for printing.